Titanium and alloys thereof are important construction materials due to their advantageous strength to weight ratio. However, these advantageous characteristics can be used only under temperatures up to about 550.degree. C. At higher temperatures structural components made of titanium or titanium alloys tend to become brittle due to the diffusion of oxygen into areas close to the surface of the structural component. When aluminum is an alloy element in a titanium alloy, the entry of oxygen into the component is delayed. Thus, efforts have been made to introduce aluminum into the surface areas of such structural components in order to form protective coatings. The process of applying such protective coatings involves a diffusion coating known as alitizing or aluminizing and this process has been especially economical.
Conventional methods or layer systems, however, have the following disadvantages. The protective coating formed by alitizing or aluminizing oxidizes at higher temperatures. Of the two metals titanium and aluminum which participate primarily in the formation of the protective layer, the aluminum has a higher affinity to oxygen than titanium. As a result, the surface of aluminized titanium components becomes coated with an aluminum oxide (Al.sub.2 O.sub.3) which forms under oxidizing operating conditions on the protective layer surface. The resulting aluminum oxide layer has practically no bonding to the titanium aluminum protective layer so that in response to any mechanical loading, the aluminum oxide layer easily flakes off, for example, due to thermal expansion when the component is exposed to temperature changes. As a result, a new aluminum oxide layer is immediately formed on the exposed areas, whereby the aluminum content of the protective layer is continuously diminished or depleted under such oxidizing conditions. When this condition continues, the thickness of the protective layer is reduced and the protection effect is diminished. Further, titanium aluminum protective coatings are brittle so that from a strength point of view such coatings must be produced as thin as possible. On the other end, the using up of the protective coating due the to repeated formation of aluminum oxide layers by oxidation requires thicker protective layers than would normally be necessary. Another disadvantage of the formation of these aluminum oxide layers and their flaking is seen in that the surface quality of the component is impaired due to a roughness that results from the flaking. Such roughness is undesirable, especially in connection with structural components forming aerodynamic profiles such as compressor blades or vanes because the roughness reduces the efficiency of such blades.